1. Field of the Invention
This invention relates to an apparatus and a method for aligning tubulars.
2. Description of the Related Art
During the construction, maintenance and repair of oil and gas wells it is necessary to connect a large number of tubulars, for example lengths of drill pipe or casing. Conventionally the upper end of a tubular is provided with a threaded socket or box whilst the lower end is provided with a threaded pin which is slightly tapered.
In practice it is very easy for the pin of one tubular to be incorrectly inserted into the socket of another tubular with the result that the threads on one or both the pin and the socket can readily be damaged.
Considerable skill is required to correctly align tubulars and historically this task has been undertaken by a highly experienced rig-hand called a “stabber”.
In order to facilitate correct alignment a device known as a “stabbing guide” is frequently used. One such stabbing guide comprises a plastic body member which can be mounted on the socket of a pipe held in slips. The plastic body member has a central passageway the upper part of which defines a funnel which leads into a lower passageway which is concentric with the socket. In use, as the upper tubular is lowered, its pin enters the funnel of the stabbing guide and then travels down the lower passageway into the socket. The stabbing guide (which comprises two semi-circular pieces hinged together around the socket) is then removed and the tubulars are screwed together and tightened to the required torque either by a power tong or a tong assembly comprising a power tong and a backup tong.
It has been observed that an accuracy in alignment of approximately 1 mm is required to inhibit problems associated with thread misalignment.
PCT Publication Number WO 98/32948, owned by the applicants for the present application, discloses an apparatus for aligning tubulars which apparatus comprises a guide mounted on one of a power tong and a backup tong.
It has been observed that the prior art apparatus, although reasonably accurate, is not suitable for multiple uses where accuracy is paramount and with little physical input from rig hands.